What shells can be used as money in ancient times?

Shells are common in the sea, but it was very difficult to go to the seaside at that time, so they were very precious and could be exchanged for goods. Later, it became the earliest coin. When it is not enough, there are the words "shell, copper shell, bone shell, baby". There are a lot of real unearthed Beibi coins, and they are extremely cheap.